全文获取类型
收费全文 | 107570篇 |
免费 | 12931篇 |
国内免费 | 8994篇 |
专业分类
电工技术 | 9536篇 |
技术理论 | 3篇 |
综合类 | 11467篇 |
化学工业 | 13283篇 |
金属工艺 | 7498篇 |
机械仪表 | 7996篇 |
建筑科学 | 8934篇 |
矿业工程 | 4122篇 |
能源动力 | 2946篇 |
轻工业 | 11572篇 |
水利工程 | 3559篇 |
石油天然气 | 3437篇 |
武器工业 | 1516篇 |
无线电 | 11940篇 |
一般工业技术 | 9402篇 |
冶金工业 | 3941篇 |
原子能技术 | 1925篇 |
自动化技术 | 16418篇 |
出版年
2024年 | 614篇 |
2023年 | 1675篇 |
2022年 | 4225篇 |
2021年 | 5494篇 |
2020年 | 3899篇 |
2019年 | 2772篇 |
2018年 | 2972篇 |
2017年 | 3292篇 |
2016年 | 2915篇 |
2015年 | 4770篇 |
2014年 | 6014篇 |
2013年 | 7310篇 |
2012年 | 8944篇 |
2011年 | 9007篇 |
2010年 | 8710篇 |
2009年 | 8375篇 |
2008年 | 8762篇 |
2007年 | 8739篇 |
2006年 | 7586篇 |
2005年 | 6279篇 |
2004年 | 4481篇 |
2003年 | 2862篇 |
2002年 | 2714篇 |
2001年 | 2398篇 |
2000年 | 1945篇 |
1999年 | 827篇 |
1998年 | 296篇 |
1997年 | 254篇 |
1996年 | 199篇 |
1995年 | 174篇 |
1994年 | 149篇 |
1993年 | 131篇 |
1992年 | 134篇 |
1991年 | 78篇 |
1990年 | 92篇 |
1989年 | 93篇 |
1988年 | 50篇 |
1987年 | 54篇 |
1986年 | 37篇 |
1985年 | 17篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 7篇 |
1981年 | 20篇 |
1980年 | 24篇 |
1979年 | 18篇 |
1959年 | 21篇 |
1951年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
3.
以智能反射面(intelligent reflecting surface,IRS)辅助的无线携能通信(simultaneous wireless information and power transfer,SWIPT)系统为背景,研究了该系统中基于能效优先的多天线发送端有源波束成形与IRS无源波束成形联合设计与优化方法。以最大化接收端的最小能效为优化目标,构造在发送端功率、接收端能量阈值、IRS相移等多约束下的非线性优化问题,用交替方向乘子法(alternating direction method of multipliers,ADMM)求解。采用Dinkelbach算法转化目标函数,通过奇异值分解(singular value decomposition,SVD)和半定松弛(semi-definite relaxation,SDR)得到发送端有源波束成形向量。采用SDR得到IRS相移矩阵与反射波束成形向量。结果表明,该系统显著降低了系统能量收集(energy harvesting,EH)接收端的能量阈值。当系统总电路功耗为?15 dBm时,所提方案的用户能效为300 KB/J。当IRS反射阵源数与发送天线数均为最大值时,系统可达最大能效。 相似文献
5.
Jiao Zhang Junjie Li Ayesha Murtaza Aamir Iqbal Lijuan Zhu Shinawar Waseem Ali Muhammad Usman Roshan Yameen Siyi Pan Wanfeng Hu 《International Journal of Food Science & Technology》2022,57(2):963-973
This work evaluated the synergistic effects of combined high-intensity ultrasound (HIU) with β-cyclodextrin (β-CD) treatments on inhibiting browning of apple juice and explored the mechanism through simulation system. The combined treatment of 300 W HIU with 0.006 g mL−1 β-CD had a synergistic impact on maintaining juice colour, resulting in a 39.06% reduction in browning degree, only a 36.64% decrease in total phenolic content, and a 17.82% reduction in PPO activity. The inhibition of enzymatic browning in simulated system revealed that HIU suppressed the enzyme (Polyphenol oxidase, PPO) and β-CD inhibited enzyme (PPO) and embedded substrate (polyphenol). The results of spectroscopic analysis showed that the particle-size distribution of PPO narrowed, the content of α-helix in the secondary structure increased, the fluorescence intensity increased, and the maximum wavelength was red-shifted after HIU and β-CD treatment. Changes in structure could further result in PPO activity loss. Hence, the combined treatment could synthetically alleviate the browning of apple juice. 相似文献
6.
该文基于掺钪AlN薄膜制备了高次谐波体声波谐振器(HBAR),研究了钪(Sc)掺杂浓度对AlN压电薄膜材料特性及器件性能的影响。研究表明,当掺入Sc的摩尔分数从0增加到25%时,压电应力系数e33增加、刚度 下降,导致Al1-xScxN压电薄膜的机电耦合系数 从5.6%提升至15.8%,从而使HBAR器件的有效机电耦合系数 提升了3倍。同时,当Sc掺杂摩尔分数达25%时,Al1-xScxN(x为Sc掺杂摩尔分数)压电薄膜的声速下降13%,声学损耗提高,导致HBAR器件的谐振频率和品质因数降低。 相似文献
7.
Fenqi Du Dongmei Yang Yue Sun Yang Jiao Feng Teng Haibo Fan 《Ceramics International》2021,47(4):4963-4971
Ultrawide band gap semiconductor materials have attracted considerable attention in recent years owing to their great potential in the photocatalytic field. In this study, Zn-doped Ga2O3 nanofibers with various concentrations were synthesized via electrospinning; they exhibited a superior photocatalytic degradation performance of rhodamine B dye compared to that of undoped Ga2O3 nanofibers. The Zn dopant replaced Ga sites via replacement doping, which could increase the concentration of oxygen vacancies and lead to enhanced photocatalytic properties. When the Zn concentration increased, a Ga2O3/ZnGa2O4 hybrid structure formed, which could further enhance the photocatalytic performance. The separation of photogenerated carriers due to Zn doping and heterojunctions were the primary causes of the enhanced photocatalytic performance. This study provides experimental data for the fabrication of high-performance photocatalysts based on Ga2O3 nanomaterials. 相似文献
8.
Kexin Jiao Laurence J. Walsh Sao Ivanovski Pingping Han 《International journal of molecular sciences》2021,22(9)
Periodontitis is a chronic complex inflammatory disease associated with a destructive host immune response to microbial dysbiosis, leading to irreversible loss of tooth-supporting tissues. Regeneration of functional periodontal soft (periodontal ligament and gingiva) and hard tissue components (cementum and alveolar bone) to replace lost tissues is the ultimate goal of periodontal treatment, but clinically predictable treatments are lacking. Similarly, the identification of biomarkers that can be used to accurately diagnose periodontitis activity is lacking. A relatively novel category of molecules found in oral tissue, circular RNAs (circRNAs) are single-stranded endogenous, long, non-coding RNA molecules, with covalently circular-closed structures without a 5’ cap and a 3’ tail via non-classic backsplicing. Emerging research indicates that circRNAs are tissue and disease-specific expressed and have crucial regulatory functions in various diseases. CircRNAs can function as microRNA or RNA binding sites or can regulate mRNA. In this review, we explore the biogenesis and function of circRNAs in the context of the emerging role of circRNAs in periodontitis pathogenesis and the differentiation of periodontal cells. CircMAP3K11, circCDK8, circCDR1as, circ_0062491, and circ_0095812 are associated with pathological periodontitis tissues. Furthermore, circRNAs are expressed in periodontal cells in a cell-specific manner. They can function as microRNA sponges and can form circRNA–miRNA–mRNA networks during osteogenic differentiation for periodontal-tissue (or dental pulp)-derived progenitor cells. 相似文献
9.
10.